The invention relates to an improved process for preparing .alpha.-.beta. unsaturated alcohols by the liquid phase catalytic hydrogenation of the aldehyde corresponding to the desired alcohol. Alcohols of this type are of commercial importance as starting materials in the flavor and fragrance industry.
When an .alpha.-.beta. unsaturated aldehyde is hydrogenated to prepare the corresponding alcohol, the hydrogenation must be effected preferentially so that little or no hydrogenation of the double bond in question occurs. To achieve this, various catalysts have been proposed for this hydrogenation. The catalyst recommended in U.S. Pat. No. 3,284,517 is platinum on carbon with divalent iron and silver as promoters. According to British Pat. No. 1,123,837 platinum with an alkali hydroxide or alkali metal alkoxide as a promoter is very suitable as a catalyst. However, U.S. Pat. No. 3,655,777 states that platinum is unsuitable as a catalyst, but that very good results can be obtained with osmium. British Pat. No. 1,439,711 describes the successful use of a platinum-cobalt catalyst.
When these known catalyst are used in conventional process for the preferential hydrogenation of .alpha.-.beta. unsaturated aldehydes, the amount of catalyst required is relatively large and the conversion of the aldehyde is often incomplete. These known methods are therefore not very attractive economically.